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The universe immediately following the Big Bang wasn’t the empty void we know today. Scientists have long theorized that the early universe was an incredibly hot “soup” reaching temperatures of trillions of degrees. Now, new experiments are providing the first direct evidence that this primordial fluid was indeed turbulent and swirling, behaving much like a superheated liquid.
In scientific terms, this dense fluid is known as quark-gluon plasma (QGP). Researchers describe it as the first and hottest fluid ever to exist. Predictions suggest that QGP was a billion times hotter than the surface of the sun, persisting for just a few millionths of a second before expanding, cooling, and coalescing into atoms. Understanding its properties offers a unique window into the conditions that existed fractions of a second after the universe’s birth.
Recreating the Primordial Soup
A recent study, conducted by physicists at MIT and CERN, reconstructed heavy-ion collisions – the type that create QGP – to explore its characteristics. The core question driving the research was how quarks, fundamental particles, move through this plasma. Do they bounce and spray like particles in a cohesive fluid, or scatter randomly like particles in a gas? The experiments took place at CERN’s Large Hadron Collider (LHC), where lead ions were smashed together at nearly the speed of light. These collisions generated bursts of high-energy particles, including quarks, and droplets of QGP resembling the matter that comprised the early universe.
Using a novel strategy to provide a clearer picture of these heavy-ion collisions than previous experiments, researchers tracked the movement of quarks through the QGP and mapped the energy of the plasma after the collisions. “Now we see that this plasma is very dense, so it’s able to slow down quarks and produce splashes and swirls like a liquid. So, the quark-gluon plasma really is a primordial soup,” explained MIT physicist Yen-Jie Lee, as reported by ScienceAlert.
Quarks traveling through the QGP transfer some of their energy to the plasma, losing speed and creating a trail, much like a boat moving through water. “As an analogy, when a boat moves through a lake, the wake is the water behind the boat that moves in the same direction as the boat. The boat has transferred momentum to that portion of the water, which ‘follows’ the boat,” explained Krishna Rajagopal, a physicist at MIT who developed a model predicting the fluid-like properties of QGP.
Detecting Subtle Ripples in the Plasma
This energy transfer creates a kind of shockwave. But, detecting these ripples within the QGP is incredibly challenging. The plasma exists for only a tiny fraction of a trillionth of a second at temperatures reaching trillions of degrees. Scientists must sift through tens of thousands of particles resulting from the collisions to identify the few that are nudged by the “wake” of the quarks. Another complication arises given that quarks typically appear in pairs with antiquarks moving in opposite directions, both creating trails that can obscure the signal from each other.
To overcome this, researchers focused on rare events where collisions produced a quark and a Z boson – a neutral particle that doesn’t interact with the QGP and leaves no trail. Analyzing 13 billion collisions, they identified approximately 2,000 events involving a Z boson. It was within these rare occurrences that they could more clearly observe the “wake” effect from a single quark.
As predicted by Rajagopal’s model, the QGP reacted like a fluid, swaying and swirling in the wake of the quark. Rajagopal described the findings as “definitive and irrefutable” evidence of the QGP’s fluid behavior, though he acknowledged that the long-standing debate about whether QGP flows and undulates like a liquid may not be entirely settled.
Implications for Understanding the Universe
This new technique offers a framework for exploring similar processes in other high-energy collisions, potentially illuminating one of the most mysterious substances in the history of the universe. “In many other fields of science, the way you study the properties of a material is by disturbing the material in some way, and measuring how that disturbance propagates and dissipates,” Rajagopal stated.
The research provides crucial insights into the state of matter that existed in the earliest moments of the universe, helping scientists refine their models of the Big Bang and the subsequent evolution of the cosmos. Further investigation into the properties of QGP could unlock deeper understanding of the fundamental forces governing the universe and the origins of matter itself.
Disclaimer: This article provides information for general knowledge and informational purposes only, and does not constitute medical or scientific advice.
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